Distributed power railroad train operation supplies motive power and braking action from a lead locomotive (or lead unit) and from one or more remote locomotives (or remote units) spaced apart from the lead unit in a railroad train. Distributed power train operation may be preferable for long train consists to improve train handling and performance, especially for trains operating over mountainous terrain.
A distributed power train control and communications system generates traction and braking commands responsive to operator-initiated control of a traction (or throttle) controller (throttle handle) or a braking controller (brake handle) in the lead unit The commands are transmitted to the remote locomotives over a radio frequency communications system (such as the LOCOTROL® distributed power train communications system available from the General Electric Company of Schenectady, N.Y.) including receiving and transmitting components at the lead and the remote units for communicating over a radio frequency link (channel).
For example, when the lead unit operator operates the lead-unit throttle controller to apply tractive effort from the lead unit, the distributed power control and communications system commands each remote unit to supply the same tractive effort. Upon execution of the received command, each remote unit responds to the lead unit with a reply message indicating implementation of the tractive effort command. The distributed power control and communications system can be configured to various operational modes that affect interaction between the lead and remote units and the implementation of lead unit commands at the remote unit.
The lead unit also sends other message types to the remote units, such as status request messages, to which the remote units respond by sending a status reply message back to the lead unit. The status reply message indicates the current operational status of the replying remote unit.
The train braking system includes a locomotive brake system in each locomotive (including the lead locomotive and all the remote locomotives) and a railcar air brake system at each railcar. The operator in the lead unit controls the locomotive brakes by positioning an independent brake handle (controller), and controls the rail car brakes by positioning an automatic brake handle (controller). Each locomotive further includes a dynamic brake system described further below.
The railcar air brake system includes a pressure sensing apparatus, a plurality of valves and interconnecting piping and brake shoes at each railcar wheel. A fluid-carrying brake pipe extending the length of the train is in fluid communication with the car brake system at each railcar. Operator control of the automatic brake handle in the lead locomotive initiates a pressure change at the lead unit that propagates along the brake pipe. The pressure sensing apparatus at each railcar detects a pressure differential relative to a reference pressure and responsive thereto initiates a brake application (if a pressure below the reference pressure is detected) or a brake release (if a pressure above the reference pressure is detected). Several seconds may be required for the for the fluid pressure change to reach each railcar of the train, resulting in uneven application of braking forces at each railcar.
The lead and remote locomotives further include a dynamic brake system controllable by the operator. Activation of the dynamic brakes reconfigures the traction motors to generator operation, with the locomotive wheels supplying rotational energy to turn the generator rotor winding. Magnetic forces developed by generator action resist wheel rotation and thus create wheel-braking forces. The energy produced by the generator is dissipated as heat in a resistor grid in the locomotive and removed from the grid by one or more cooling blowers. Use of the dynamic brakes is indicated to slow the train when application of the locomotive independent brakes and/or the railcar air brakes may cause the locomotive or railcar wheels to overheat or when prolonged use of the independent brakes and/or the railcar brakes may cause excessive wheel wear. For example, the dynamic brakes are applied when the train is traversing a prolonged downgrade.
In a distributed power train, in addition to regulating the brake pipe pressure to effect application and release of the railcar brakes, operation of the automatic brake handle in the lead unit commands remote unit brake applications and releases by transmitting a brake application/release signal to the remote units via the communications channel. If the communications link between the lead and remote units is operative, the remote units receive the brake application signal and initiate brake pipe venting from their location in the train. Since each remote unit receives the brake application command before it senses the brake pipe pressure change, the railcar brakes are applied sooner than if the brake application signal is carried only over the brake pipe. Braking is thus accomplished by venting the brake pipe at the lead and remote locomotives, accelerating the brake pipe venting and application of the brakes at each railcar, especially for those railcars near the end of the train. If the communications link between the lead and remote locomotives is operative, the brake release command received by each remote locomotive is executed at each remote locomotive by charging the brake pipe to a nominal pressure, thereby releasing the rail car brakes and advantageously reducing the time required to recharge the brake pipe.
When the lead operator applies the dynamic brakes of the lead unit, an appropriate communications signal is transmitted to the remote units to activate the dynamic brakes at each remote unit. A dynamic brake release signal is similarly transmitted from the lead unit to the remote units.
In general, traction and braking messages sent over the communications system result in the application of more even tractive forces to the railcars and improve braking performance, as each locomotive can effect a brake application or release at the speed of the RF signal, rather than the slower speed at which the pneumatic brake pipe braking signal propagates along the train.
If the communications system is inoperative or the communications link between the lead unit and one or more remote units is disrupted (for example, if line-of-sight directivity is lost due to track topology or an interfering object), lead initiated braking and traction commands are not received by the remote unit(s). In particular, if the lead operator commands a return to tractive effort from a dynamic brake application, the remote units will not receive the tractive effort command. The lead unit applies tractive effort while the remote units are in a dynamic braking mode. This situation generates substantial in-train forces that can break the train and/or cause a train derailment. As operating trains grow heavier and longer, the likelihood of a train break or derailment is greater.